FI63607B - FREQUENCY REFRIGERATION FOR CELLULOSE MASS IN UTBYTESOMRAODET 65-95% - Google Patents

Description

155 ^ 1 [B] (11) ADVERTISEMENT ,,. 07 WTjB l J '; UTLÄGGN INCSSKRIFT 6 O O U / c .... Patent granted 11 07 1985 ^ Patent meddelat ^ ^ (51) Kv.lk?/lnc.CI.1 D 21 C 3/00,; FINLAND — FINLAND (21) p »*« »ttihtk« wi · —νμμμνβμπι 752631 (22) Hakamltpliv · - Ameknlngtdag 19 * 09.75 (23) AlkupUvl — GIM | h «skin | 19.09.75 (41) Interpreters | ulklMkil - Bltvlt offancMg 2U 03 76 Μ — I- |. r.klmrih.llltut M '8,

Patent · och reglsterttyreleen 'AmMcm uti «fd och utUkrHtm pubHcmd ^ .10.0.3 (32) (33) (31) FjTdatty atuoikaut —8« fird prlorkoC 23.09.7 ^ +

Sweden-Sweden (SE) 7 ^ + 119 ^ + 9-6 (71) Mo och Domsjö Aktiebolag, Fack, S-891 01 Örnsköldsvik 1,

Sweden-Sweden (SE) (72) Jonas Arne Ingvar Lindahl, Domsjöverken, Lars Gustaf Rudström,

Domsjöverken, Sweden-Sweden (SE) (7 * +) Berggren Oy Ab (5 * +) Method for producing cellulosic pulps in the yield range 65-95% -Förfarande för framställning av cellulosamassor i utbytesomrädet 65-95%

The present invention relates to a process for the production of bleached cellulosic pulps with a yield of between 65 and 95 $ starting from reduced, washed lignocellulosic material.

In the pulp industry, the amount of yield is becoming increasingly important as the supply of raw material becomes more difficult. However, the yield must not be increased at the expense of the quality of the pulp and the manufacturing costs, nor without taking environmental considerations into account. The object of the present invention is, while maintaining a high yield, to improve both the environmental impact of the process and the quality of the pulp, as well as to reduce the manufacturing cost. By applying the present invention, the range of use of the pulp is also expanded.

It is known to produce a high-yield pulp by compressing the chips jr by repeatedly releasing the pressure in a screw press and then expanding by reducing the pressure, whereby a chemical solution (sodium peroxide or sodium sulphite) is injected into the chips. However, when using this method, the brightness of the pulp does not improve compared to a conventional mechanical pulp made by grinding and then bleaching.

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The production of mechanical pulps by grinding wood in the presence of bleach waste liquor is already known, in which case fresh bleaching chemicals can also be used and the defibering can alternatively be carried out in a plate grinder or in a so-called FROTAPULPEF. The pulp obtained according to this method acquires better strength and brightness than conventional groundwood, but in these respects it does not compare with chemically produced pulps.

It is further known to grind pulp in a disc mill at high consistency. Grinding is performed without the addition of liquid at an overpressure of up to 980 kPa in plate grinders, where the pieces of material are subjected to torsional forces which divide them into private fibers (intermediate levels of the original fibers) covered with lignin or the like. Although this method gives 50-90% yields of relatively long-fiber pulp, this result must be weighed e.g. against the deterioration of color which occurs at high temperatures during relatively dry grinding. Thus, the brightness of the resulting pulp is low and contains a relatively large amount of impurities, but the method offers certain economic advantages due to its low equipment requirements and a certain time gain.

The method according to the present invention is not troubled by the above-mentioned drawbacks.

Accordingly, the present invention is directed to a process for producing cellulosic pulp in a yield range of 65-95% from reduced, washed lignocellulosic material such as wood chips, sawdust or the like, using either steam heating or slight dissolution in the presence of known lignite removal , continuing the treatment until the desired pulp yield is achieved, defibering the treated material under pressure or in one or two stages in plate mills or other defibering equipment suitable for reduced cellulosic material, diluting and cooling the material before, during or after the first defibering, followed by sieving and dewatering , while the heavy metals are separated in a complex-bound water-soluble form, after which the resulting cellulosic material is bleached in one or two steps, primarily so-called lignin is preserved. oxidizing and / or reducing bleaches, and subjected to the thickening following each bleaching step, and the process is characterized in that the cooled bleaching effluent having a pH of 6-12, preferably 6.5-10, is returned to the diluent and coolant, and that after this use, the bleach waste liquor is completely or partially regenerated together with the recovered liquids and waste liquors to recover the chemicals and fuel value contained therein.

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The method according to the invention has the advantage that the consumption of bleaching chemicals is significantly reduced compared to the prior art, which reduces costs and environmental pollution. In addition, a pulp with even better strength is obtained, which makes it possible to produce paper with a lower basis weight while maintaining its strength properties. In addition, the pulp produced according to the invention mixed with a chemical pulp such as sulphate or sulphite pulp requires a smaller amount of chemical pulp than known pulps in order to achieve a certain level of strength and brightness, as a result of which the production cost of such paper is reduced. The resulting pulp is suitable as a raw material for papermaking over a wider and more varied range of quality requirements than is currently normal for pulps in this yield range, depending on the better purity, brightness and strength of the pulp according to the invention and its higher absorbency than the prior art.

The method according to the invention will be explained in more detail in connection with the accompanying flow chart.

The reduced and preferably washed cellulosic material, e.g. wood chips, is introduced into a receiving tank 1, from where it is further fed to a roasting vessel 2, where it is treated for a certain time with steam (roasting) at atmospheric pressure. The roasted material is further fed to a tank 3 with a screw feeder, where it is then continuously expanded with a lignin removal solution, e.g. a bisulphite solution, and is allowed to fall to the bottom of the tank. The material impregnated from the tank 3 is transferred to a digester equipped with a feeder where it is passed through it in the steam phase until the desired yield is reached, after which the cooked material is defibered in a fiberizer 5, e.g. a plate mill, in the presence of cooking chemicals and mainly at previous temperature. The defibered material is diluted and cooled with bleach waste liquor 6, passed through a leveling vessel 22 and transferred to a screen compartment 7j from which the screened fibrous slurry is pumped to a dewatering compartment 8. The resulting waste liquor is passed to a collection vessel 18. As the material travels between the above compartments, heavy metal ions are added. Once the fibrous slurry has been dewatered, it is subjected to so-called lignin-preserving bleaching with oxidizing or reducing bleaching agents in the bleaching tower 9, and may undergo another dewatering step 14. The resulting pre-bleached pulp is exported for drying or directly to papermaking. The bleach waste broth in the dewatering step 14 is passed to a collection tank 17- “63607

Another particularly suitable embodiment of the present invention is shown in FIG. If necessary, the pH of the material in the hydrocyclone is adjusted by stirring the appropriate solution 16 in the bleach waste broth before it enters the cyclone. The stream of hydrocyclone material is passed through the reaction tank 23 and then either directly to the screen compartment 7 or via a second defibering device 12 and a leveling vessel 2H to the screen compartment 7 ·

According to a suitable embodiment, the material from the defibering device 5 diluted and cooled by the bleaching effluent 6 is passed through a leveling vessel 22 via a washing device 19 to a screen compartment 7. This also applies to the effluent streams from the hydrocyclone 10 or another defibering device 12, as shown in Figure 1. led to a recovery facility 20.

According to a suitable embodiment of the method according to the invention, which is also shown in Figure 1, the fibrous material from the second dewatering step 14 is subjected to additional bleaching in the second bleaching step 13 with reducing bleaches, preferably using so-called lignin-preserving bleaching. However, if oxidizing bleaches are used, the resulting bleach waste liquor is passed to a collection vessel 17. · The waste liquor from the reducing bleaching step 13 is led to a recovery plant 20 via a dewatering step 25 and a collection vessel 27. The pre-bleached pulp is preferably fed directly to the paper machine 26.

Since peculiar pulp grades are obtained by starting from different types of wood or other cellulosic materials using the process according to the invention, it may also prove advantageous to return the bleach waste liquor to more than one point in the process in order to obtain the best possible end product in each case. Such modifications of the method are, in principle, self-evident, so that they will not be explained in more detail. However, a modification suitable for thermomechanical pulping should be briefly mentioned here. In these processes, as mentioned above, no lignin removal chemicals are used before the first defibering step 5, but the washed raw material is fed from the receiving tank 1 either directly or via the roasting vessel 2 to the digester 4. The bleaching broth can then suitably be added before or during the first defibering step.

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Suitable lignin removers for the slight dissolution of the present invention include, for example, sodium bisulfite, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, etc. Neutral and alkaline oxygen gas dilution can also be suitably used. By slight dissolution is meant, according to the invention, dissolved at temperatures between 80 and 180 ° C and at overpressures between 0 and 1900 kPa. The dissolution is continued in each case - largely depending on the cellulose raw material - for such a time that the desired yield is reached, i. usually until a Kappa number between 50 and 150 is reached.

First stage defibering according to the invention. at or under pressure is carried out in a defibering device suitable for the reduced lignocellulosic material, which may be, for example, a plate mill. Pulping. is carried out at a temperature between 80 and 180 ° C and an overpressure between 0 and 1800 kPa.

In the case where the defibered pulp is treated in a hydrocyclone, the pulp from the hydrocyclone can, if considered desirable, be treated in a second defibering unit at a temperature between 40 and 100 ° C, preferably between 80 and 90 ° C and atmospheric pressure. A suitable fiberizing device for this purpose is, for example, a plate mill, cone mill or helical fiberizing device, so-called FROTAPULPERS. The residence time in the reaction vessel between the hydrocyclone and the second fiberizing unit is preferably

During strong mechanical defibering, heat is generated, which results in high temperatures being reached during processing.

In this case, when the material is regretted in the first stage, an excess of lignin scavenger must be present, which retains the initial tendency of the lignocellulosic material to discolour. Due to the wear of the work surfaces of the equipment, for example the grinding plates of the disc refiner, the concentration of heavy metal ions such as Fe, Mn, Ni, Cu, etc. in the defibered material increases, which spoils the color of the material. To counteract this negative effect, complexing agents of said metals are added prior to pulp bleaching. When, according to the invention, an excess of bleaching waste slurry is added to the pulp after its grinding, a certain advantageous formation of a complex of heavy metal ions is already achieved, which results in a lighter pulp. In practice, even before bleaching, slightly more complexing agent is often added than would theoretically be necessary to bind undesired metals into complexes. The underdose of the complexing agents may be in the range of 6,660,607 relative to the brightness of the pulp. If the bleaching is carried out with peroxide or another oxidizing bleaching agent, organic acids are also obtained in the bleaching waste liquor, some of which may form complexes with metal ions.

Suitable oxidizing bleaches for bleaching according to the invention include hydrogen peroxide, sodium peroxide, peracetic acid, oxygen, ozone and the like. Suitable reducing bleaches include dithionite (hydrosulfite), sulfur dioxide, bisulfite, sulfite, hydroxylamine, hydrazine, thiourea, thioglycolic acid and the like. Preference is given to bleaching agents which provide so-called lignin-preserving bleaching.

When peroxide is used in bleaching, the bleaching broth contains residues of peroxide (0.1 to 1.0 g H 2 O 2 per liter) and by reusing it as a diluent and coolant according to the invention, these residues are utilized in bleaching the cellulosic material or maintaining its brightness during the process. The peroxide bleaching effluent usually also contains water glass, sodium hydroxide and traces of magnesium sulfate. Said chemicals have a stabilizing effect on hydrogen peroxide and increase the pH of the fibrous waste. If the fibrous slurry is still defibered in the second step, the second defibering can be performed at a higher pH than if no bleach residue is added after the first defibering step.

In the event that the bleach effluent comes from a reducing bleaching step in which the bleaching agent is dithionite, the effluent contains sulphite, bisulphite, thiosulphate, small amounts of dithionite and complexing agents which are stage of the process.

When the alkaline bleaching slurry is used in the second defibering step, a stronger pulp is obtained than when the defibering is performed in a weakly acidic or acidic environment. The possibility to adjust the pH of the bleaching broth used as a diluent and coolant, if necessary, is therefore included in the process according to the invention.

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After pressurized defibering according to the prior art, the fibrous slurry is usually passed to a cyclone, which separates the excess steam from the defibered material and the cooking chemical residues. Cold water is added for dilution and cooling, and the extractants dissolved during fic cooling are precipitated as particles and adhere to the fibers. Such a resin can cause large resin deposits in pulp mill equipment such as pumps, pipelines and wires, and poses an obvious problem. However, it has surprisingly been found that significantly less or no resin precipitates if, according to the present invention, an alkaline bleach waste slurry is added to the fibrous slurry after pressure fiberization. It is particularly advantageous to add the bleach waste liquor in the cyclone to obtain a good and homogeneous mixture between the fibrous slurry and the added bleach waste liquor.

Although no theoretical explanation can be given for the effect thus obtained, it is possible that the added waste liquor forms soaps with the resin and fatty acids normally contained in wood cellulose. Such formation of sodium soaps is facilitated by the fact that the added complexing agents have reduced the concentration of heavy metal ions that would otherwise have formed hard metal soaps that are more difficult to disperse than sodium soaps.

Since one of the purposes of adding liquid to the cyclone is to cool the fibrous slurry from the defibering, the bleach waste liquor must be cooled. However, the degree of cooling depends on the temperature at which the bleaching is performed. The bleach waste broth can then be suitably placed in a heat exchanger (21 in Fig. 1) to heat fresh cold water. The heated fresh water can then be used to make the necessary cooking and bleaching solutions in the process. Of course, a small partial stream of bleaching broth can also be used for the latter solutions.

When recovering delignification chemicals by first or second fiberization steps. after, the added bleach broth is recovered at the same time. Since the lignocellulosic material is normally diluted with water after the first defibering step, the addition of the bleaching waste liquor according to the invention causes a higher than normal concentration of chemicals and organic matter to be recovered, which at the same time increases the calorific value of the waste liquor. The recovery of bleaching effluent 63607 achieves a significant improvement in the environment, as the biochemical oxygen demand (BODy) of the bleaching effluent discharged into the sewer can be up to 15 ~ 20 kg per tonne of bleached pulp. According to the invention, the recovery of BOD is 50-70% lower than in previously known methods.

In the event that the cooking sludge is not recovered, the invention provides a lighter and more environmentally friendly waste sludge, due to the fact that the added bleaching sludge contains bleach residues. It is particularly advantageous in this case if the bleach waste broth contains peroxide residues which promote the decomposition of organic compounds during external cleaning, for example in a swimming pool.

In the event that no cooking chemicals are present in the process but only bleaching chemicals, the bleaching waste broth can be transferred to an external recovery plant and regenerated therein (cross-recovery).

The following application examples illustrate both the production process according to the invention and the even better properties of the cellulose pulps produced by this process.

Example 1

In the apparatus of Figure 1, washed spruce chips with piece dimensions of 40 mm in length, 20 mm in width and 3 mm in thickness were treated with atmospheric steam for 15 min. The roasted chips were fed into a tank with a feed coil and impregnated with sodium bisulfite solution during their expansion in the tank. The composition of the bisulfite solution was 65 g NaOH and 68 g SO2 per liter and had a pH of 6.0. The saturated chips were then boiled in the steam phase for 20 min at 160 ° C and defibered in a plate mill at the same temperature with a pulp consistency of 40% to a freeness value of 650 ml. Preeness is a measure of mass flow resistance and was measured by the Canadian Standard Preeness Method (CSF). The pulp yield was 89.0%.

A subsample (A) of the defibered pulp was diluted with water to a pulp consistency of 20% and defibered in a plate mill.

A second aliquot (B) of the same mass was diluted with bleach waste liquor containing 0.8 g H 2 O 2, 0.5 g NaOH, 2.5 g Na 2 SiO-j, 0.03 g

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9 63607 diethylenetriaminepentaacetic acid (DTPA) and 0.02 g MgSO 4 per liter of waste liquor. In addition, the bleach waste liquor contained an unknown amount of oxidized organic matter, consisting mainly of zero fibers and organic acids. The pH of the bleaching broth was 8.8. After a reaction time of 5 minutes at 75 ° C, subsample B was defibered in the same manner as subsample A. Both samples were sieved and then thickened in the same manner. Both samples were tested in the same manner and the results are shown in Table 1 below.

table 1

Properties tested Sample A Sample B

Preeness, CSF ml 200 205

Fiber size distribution in the Bauer McNett classification: + 20 mesh% 8 7.5 + 150 mesh% 70 73.5 - 150 mesh% 22 19

Brightness, SCAN% 62.3 66.1

Breaking length m 3900 4800

Tear coefficient 69 74

Absorption capacity (g water / g mass) 9.3 12.1

It is clear from the results that the pulp made according to the invention is lighter and stronger than the conventionally produced pulp. In addition, the pulp according to the invention has a higher water absorption capacity - a factor which is of great importance in many fields of application. In addition, the method according to the invention has obtained a more favorable fiber size distribution, which is evident from the increased proportion of fibers remaining on the 150 mesh wire.

Subsequent single-stage bleaching of the sample masses A and B for 60 min with 0.8% Na2S2Oi | (dithionite), calculated on abs. by weight of dry pulp, at 70 ° C and 4% pulp consistency the following brightness values were obtained: Sample A (% SCAN): 67.3 Sample B (% SCAN): 71.0

In one-step bleaching of the second portion of the finished sample masses with a hydrogen peroxide solution containing 2% H 2 O 2, 4% Na 2 SiO 3, 1.5% NaOH and 0.05% MgSO 4, abs. based on the weight of the dry pulp, which lasted 120 minutes and occurred at 12% of the pulp consistency, the following brightness values were obtained: 10 63607 Sample A (% SCAN): 69.5 Sample B (% SCAN): 71.8

The results show that both reductive bleaching with dithionite and oxidative bleaching with peroxide give a lighter end product starting from the pulp prepared according to the invention than starting from the pulp prepared according to the prior art. Thus, by using the bleaching waste broth of the invention, the addition of fresh bleaching chemicals can be reduced and the brightness of the pulp can be maintained.

Example 2

Washed pine chips with piece dimensions of 40 mm, 20 mm and 3 mm were roasted in the plant of Figure 1 with steam at atmospheric pressure for 15 minutes and impregnated in tank 3 as it swelled with a bisulphite solution containing 75 g NaOH and 72.1 g SC per 2 liters . The pH of the solution was 6.2. The chips thus saturated were then boiled in the steam phase in a digester for 4 to 20 minutes at 160 ° C. The dissolved chips were then defibered at the same temperature and vapor pressure in a plate mill to 800 ml Freeness. The pulp yield was 90.1%.

A sub-sample (A) of the defibered pulp was diluted with pure water to a pulp consistency of $ 18 and defibered in a plate mill.

A second aliquot (B) of the same mass was diluted with bleach waste liquor containing 0.6 g H2O2, 0.7 g NaOH, 2.0 g Na2SiOj, 0.03 g DTPA and 0.02 g MgSO || per liter. In addition, the bleaching broth contained oxidized organic matter in the same manner as in Example 1. The pH of the bleaching broth was 9.5 · After a reaction time of 5 minutes at 750c, this subsample was defibered in the same manner as subsample A. Both samples were then sieved and thickened in the same manner. The test results are shown in Table 2 below.

Table 2

Properties tested Sample A Sample B

Freeness, CSF ml 240 250

Fiber size distribution in the Bauer McNett classification: + 20 mesh% 19.1 18.4 + 150 mesh% 53.7 55.4 - 150 mesh% 27.3 26.2

Ti kc content, SOMMEKVILLE <0.15 mm% 0.16 0.03

Brightness, SCAN% 54.5 62.3

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As can be seen from the results, in this case too a more favorable fiber size distribution was obtained by the method according to the invention. In addition, the stick content was significantly reduced. An additional advantage is the high brightness of the unbleached pulp, which is achieved by the method according to the invention.

Both subsamples were then bleached with peroxide in the next step. In this case, 1.5% # 2 ^ 2 »3 Ϊ Na2SiO-j, 1.3%

NaOH and 0.05% MgSO 4, all abs. calculated on the dry weight. The bleaching time was 120 minutes and the consistency of the pulp was 12%. The subsamples were tested in the same way and the results are shown in the following Table 3-

Table 3

Properties tested Sample A Sample B

Brightness, SCAN% 60.2 68.2

Ethanol extract% 0.54 0.15

Breaking length m 3300 4300

Tear coefficient 70 78

Absorption capacity (g water / g mass) 10.2 13> 3

The results shown in Table 3 show that the bleached pulp produced by the process according to the invention has a significantly better brightness and a much lower extract content than the pulp produced according to the prior art. Moreover, it is clear that both the strength and the absorbency are considerably better when the production is carried out by the method according to the invention.

The invention has been illustrated in the above examples in connection with so-called chemimechanical pulping processes, but the invention is not limited only to this type of processes, but can also be applied to so-called thermomechanical pulping processes, i. to those in which dissolution does not occur in the presence of chemicals.

In summary, the advantages obtainable by the method according to the invention mean that the production cost of the pulp becomes lower than what can be achieved with the prior art. In order to achieve a certain brightness, the consumption of bleaching chemicals can be reduced, and as the pulp becomes stronger, paper lighter than its surface pressures can be produced, while maintaining the properties. If the paper is to be made from a mixture with chemical pulps such as sulphite or sulphate pulps, the proportion of 63607 chemical pulp can be reduced. The end result is paper with the same quality and properties, but lower manufacturing costs. The extract content is substantially reduced, which is important for obtaining paper with good absorbency and brightness stability, and is advantageous for avoiding resin deposits, especially in papermaking. Further profit is obtained in the form of recovered chemicals. Not least important is the significant improvement achieved with respect to the environment in the practice of the present invention.

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Claims (7)

13 63607 A process for producing a cellulosic pulp in the yield range from 65 to 95% of reduced, washed lignocellulosic material of bays, such as wood chips, sawdust or the like, either by steam heating or by slightly dissolving in the presence of both known and the yield is obtained by defibering the treated material under pressure or pressure in one or two stages in plate grinders or other defibering equipment suitable for reduced cellulose material, by diluting and cooling the material before, during or after the first defibering, followed by sieving and dewatering while separating heavy metals into the complex in a bound aqueous solution, after which the resulting cellulosic material is bleached in one or two steps, primarily using so-called lignin-preserving bleaching, with oxidizing and / or with bleaching agents, and is passed to the thickening following each bleaching step, characterized in that the cooled bleaching liquor having a pH of 6-12, preferably 6.5-10, is returned to the diluent and cooling liquid, and that the bleaching liquor is completely or partially regenerated together after this use with recovered liquids and waste liquors to recover the chemicals and fuel value contained therein. Process according to Claim 1, characterized in that the material from the first defibering device is treated in a hydrocyclone in the presence of a continuously diluting and cooling bleaching liquor to which a suitable pH-adjusting solution is added, after which the cellulosic material thus obtained is reacted with the bleaching effluent before either processed in another defibering unit or passed directly to the screen compartment. Process according to Claims 1 to 2, characterized in that fresh bleaching chemicals are additionally added to the bleaching effluent used as diluent and coolant. Process according to Claims 1 to 3, characterized in that the bleach waste liquor used as diluent and coolant is regenerated together with the cooking waste liquor. 14 63607 Process according to Claims 1 to 4, characterized in that complexing agents are added to the fibrous slurry as it passes from the screen compartment to the thickening compartment before bleaching. Process according to one of the preceding claims, characterized in that the fibrous slurry resulting from the thickening of the first bleaching step is further bleached with reducing or oxidizing bleaching agents such as dithionite (hydrosulphite e.g. Na 2 S thioglycolic acid or hydrogen peroxide, sodium peroxide, peracetic acid, oxygen or ozone, respectively. 1. The use of cellulosic material in the form of a mixture of 65-95% of the resultant cellulosic material, in which case the lignocellulosic material is present in the liquid, in which the genome is obtained by means of a solid or other formulation närvaro ay delignifieringsmedel pä känt sätt och under en tidsperiod tills önskat massautbyte erhällits, tryck- eller trycklös defibrering i ett eller tvä steg av det behandlade materialet ellegynering or ellor förderdelat cellulosamerre-finger defibrating of the material upstream and downstream of the material, under the same conditions as the tungsten metal in the complex wadding form, after which the cellulosic material is used for the purpose of testing and replacing the genome lignin-beyarande blekning, medelst oxiderande och / eller reducerande blek-medel samt leds en en varje bleksteg feljande avvattning, kännetecknat av to nedkyld blekavlut med et pH av 6-12, företrädesyis 6,5-10, äterförs säsom späd- oc- and after which the anthelmintic is treated with the same or more than one year of the same type of chemical and brandy. Il: